Adjacent solid boundaries alter the size of regurgitant jets on Doppler color flow maps

Recent studies have attempted to predict the severity of regurgitant lesions from jet size on Doppler flow maps. Jet size is a function of both regurgitant volume and fluid entrained from the receiving chamber and, for a free jet, is a function of its momentum at the orifice. However, regurgitant jets often approach or attach to cardiac walls, potentially altering their momentum and ability to expand by entrainment. Therefore, this study addressed the hypothesis that adjacent walls influence regurgitant jet size as seen on Doppler flow maps. Steady flow was driven through circular orifices (0.02 to 0.05 cm2) at physiologic velocities of 2 to 5 m/s. At a constant flow rate and orifice velocity, orifice position was varied to produce three jet geometries: free jets, jets adjacent to a horizontal chamber wall lying 1 cm below the orifice and wall jets with the orifice at the level of the wall. Doppler color flow imaging was performed at identical instrument settings for all jets. Two long-axis views of the jet were obtained: a vertical view perpendicular to the wall, resembling that most commonly used in patients to image the length of the jet, and a horizontal view parallel to the chamber wall. Velocities along the jet were also measured by Doppler mapping. Jets with their orifices adjacent to the wall but not at its level were deflected toward the wall proximally (the Coanda effect), increasing jet area in the vertical plane by 8 ± 4% compared with corresponding free jets (p < 0.001), with no change in area in the horizontal plane. Wall jets with their orifices at the level of the wall were 34 ± 5% smaller in area than free jets in the vertical plane (p < 0.0005) and 13 ± 6% larger in area in the horizontal plane (p < 0.005). Distal velocities in jets encountering walls were higher than those of free jets (p < 0.0002). Therefore, in the views perpendicular to walls (vertical views) most commonly used in vivo for imaging jets near cardiac structures, a jet lying along the wall will appear smaller than a free jet produced by the same regurgitant flow. The wall jet can entrain fluid and expand only on one side and it spreads laterally over the surface to a greater extent than usual. The area of a deflected jet is slightly increased by the Coanda effect, which draws the proximal jet toward the wall. Therefore, jet size cannot be related to the degree of regurgitation without considering jet geometry and adjacent walls.